Light-emitting diodes (LEDs) are new generation of lighting elements, which has advantages of power-saving and long life etc., so they have been widely used in various devices, especially used in backlight modules of flat panel displays, such as liquid crystal displays.
Light emitting diode strings of flat panel displays have to be driven via driving circuits to make the light emitting diodes to emit light. But each light emitting diode has its own load characteristics of voltage-current curve; therefore, different electrical currents would be produced to flow through the light emitting diodes even though the light emitting diodes are driven by a same driving voltage. When electrical currents through different light emitting diodes are different, the light emitting diodes would have different brightness. So, a number of light emitting diodes are electrically coupled to each other in series to ensure that a same electrical current flows through the light emitting diodes to make the light emitting diodes with a same brightness.
The more the light emitting diodes electrically coupled in the light emitting diode string, the greater the DC voltage to drive the light emitting diode string is. Unfortunately, components in the driving circuit can only withstand a certain voltage value. For a larger display panel, since the amount of the light emitting diodes in each light emitting diode string is limited, so plural light-emitting diode strings are used to achieve the lighting purpose. Correspondingly, more steady flow circuits and control circuits must be used in the lager display panel, or high-voltage electronic components can be used to form the driving circuit in the larger display panel. However, cost is inevitably increased in both of the approaches, and even some of the associated solutions would make control circuits more complex for achieving illumination uniformity.